DYNAMIC FRACTURE MECHANICS: NEW EXPERIMENTAL AND NUMERICAL METHODOLOGIES

摘要

Drop weight or pendulum machines are frequently used to determine the dynamic fracture toughness of a material.rnDetermination of the dynamic fracture toughness requires an analysis of the experiment, but unfortunately the boundary andrnloading conditions are not directly measurable in these tests or have a degree of uncertainty making the analysis difficult. Arnnovel dynamic fracture test that overcomes many of these difficulties is described. A gas gun launches a striker bar at arnknown speed that impacts a transmitter bar in contact with a pre-cracked three-point bend specimen and fractures thernspecimen. The specimen is instrumented with a crack ladder gage, crack opening displacement gage and strain gages. Arnfracture mechanics model is used to determine the dynamic fracture toughness. Further, a dynamic fracture mechanicsrnmethodology is implemented into the Lagrangian finite-element hydrocode EPIC. The generalized energy release rate T* isrnassumed to be a measure of the crack driving force. This representation for the crack driving force was selected because itsrngenerality includes elastic-plastic behavior and inertial effects. It is particularly well suited for implementation into EPIC. Inrnaddition to the introduction of the crack driving force, a nodal release algorithm to model the formation of traction-free surfacesrnproduced by a propagating crack was incorporated into the program.